Currently, portable wireless terminals typified by a W-CDMA (Wideband Code Division Multiple Access) comfortable with 3GPP (3rd Generation Partnership Project) standard or a so-called third generation portable telephone have been put to practical use. The W-CDMA is a so-called CDMA (Code Division Multiple Access) system that establishes a communication using the spread spectrum technique. As compared with a conventional second generation portable telephone system such as a PDC (Personal Digital Cellular) telephone, the W-CDMA has such advantages as a large channel accommodation capacity and a high transmission rate. Due to this, advanced nations in which frequency resources are tight and high value added communications are required have competed to introduce the W-CDMA terminals.
Differently from the second generation portable telephone, even if a W-CDMA terminal communicates with a base station in a cell adjacent to a cell in which the W-CDMA terminal is present, then the W-CDMA terminal can communicate with the adjacent other base station with the same frequency by changing a spreading code that is a feature of a CDMA communication without need to change the frequency. Due to this, the W-CDMA terminal can easily access a plurality of base stations simultaneously, simultaneously connect to the base stations by lines, and secure a communication line without interruption. It is thereby possible to realize hand-over without intermittent sound or so-called “soft hand-over” even during the hand-over for switching a communication destination from one base station to another base station during moving of the W-CDMA terminal among the cells.
Meanwhile, it is important for the W-CDMA terminal to grasp a moving velocity of the terminal so as to improve communication quality for the following reasons. In a RAKE receiver employed in a W-CDMA terminal, an internal correlator (a searcher) searches delay profiles of incoming waves including reflected waves from the respective base stations, and finds and gives weights to several strong incoming waves, a secondary demodulator in rear of the searcher decodes data on the weighted strong incoming waves, and the decoded data is used for reception.
A delay profile strongly depends on a reception environment of each mobile station. Although the delay profile basically remains unchanged in a stationary state, the incoming wave is greatly changed by multipaths according to moving locations in a moving state.
Due to this, in the moving state as compared with the stationary state, it is necessary to allow the searcher to always operate and to accelerate a following velocity of the searcher if the moving velocity of the terminal is higher. Nevertheless, to accelerate the following velocity of the searcher means to increase a calculation amount of a searcher-related circuit. From viewpoints of power consumption saving, it is desirable to reduce the calculation amount to an appropriate amount when the moving velocity is low.
Moreover, multipaths change greatly in the moving state as compared with the stationary state. Accordingly, it is necessary to reduce averaging processes performed when each delay profile is calculated in the moving state. On the other hand, since multipaths do not change in the stationary state, it is desirable to increase the averaging processes so as to suppress the influence of noise and the like.
Furthermore, since the multipaths do not change in the stationary state, it is preferable to allocate the strongest incoming wave to each finger. However, in the moving state, new incoming waves such as reflected waves arrive in succession because of the change of moving points whereas the incoming waves that have been strong previously gradually weaken with passage of time. Therefore, in some cases, as the incoming wave allocated to each finger, it is appropriate to select not the strongest incoming wave but an incoming wave that is currently weak but is gradually intensified.
Generally, there is a limit to the number of fingers. Due to this, different algorithms are used to determine to which fingers the numerous incoming waves are to be allocated, depending on environmental conditions such as the moving velocity stated above. Therefore, it is important to grasp the moving velocity of the portable wireless terminal so as to satisfy both low power consumption and improvement of communication quality. In these circumstances, several methods of detecting the moving velocity have been proposed conventionally.
The first example of the conventional techniques for measuring a moving velocity is disclosed in JP-A-7-111675 identified herein as Patent Document 1 and entitled “method and device of positioning mobile object and mobile communication system using the same”. The Patent Document 1 proposes the following technique. A portable wireless terminal transmits a radio wave with a predetermined frequency first. Next, a plurality of base stations receives the radio wave transmitted from the portable wireless terminal. The radio wave received by each of the base stations includes Doppler shift resulting from movement of the portable wireless terminal. A moving direction and a moving velocity of the mobile body are estimated from a spatial distribution status of Doppler shift amounts detected at the respective base stations.
The second example of the conventional techniques is disclosed in JP-A-10-261989 identified herein as Patent Document 2 and entitled “portable telephone device”. The Patent Document 2 proposes the following portable wireless terminal. A portable wireless terminal observes an electric field (hereinafter, “field”) level of a received signal during diversity reception and detects a fading frequency (f) from a temporal change of the field level. It is known that a correlation of f=V/λ is held among this fading frequency, a wavelength (λ) of the received signal, and a moving velocity (V) of the portable wireless terminal. The moving velocity (V) is calculated using this relational expression.
The third example of the conventional techniques is disclosed in JP-A-11-98071 identified herein as Patent Document 3 and entitled “CDMA mobile wireless terminal device”. The Patent Document 3 proposes a technique for calculating a Doppler frequency caused by fading from a spreading width of a carrier frequency of a received signal from each base station, and for calculating a moving velocity of the CDMA mobile wireless terminal device from the carrier frequency and the Doppler frequency.
The fourth example of the conventional techniques is disclosed in JP-2669288 identified herein as Patent Document 4 and entitled “microcell/integrated microcell mobile communication system”. The Patent Document 4 proposes the following technique. First, a plurality of base stations transmits wireless control channel signals to a portable wireless terminal in a time division fashion. Next, the portable wireless terminal in a waiting state measures received field levels of the wireless control channels from the respective base stations, and estimates its moving velocity from changing speeds of the received field levels of the wireless control channels from the respective base stations.
The fifth example of the conventional techniques is disclosed in JP-A-2004-104223 identified herein as Patent Document 5 and entitled “portable communication terminal and method of detecting moving velocity of portable communication terminal”. The Patent Document 5 proposes the following technique. A portable communication terminal estimates its position from field levels of received signals or the like in advance, and calculates its moving direction and its moving velocity from the position information and Doppler shifts included in the signals from respective base stations.
The sixth example of the conventional techniques is disclosed in JP-3019800 identified herein as Patent Document 6 and entitled “portable telephone set”. The Patent Document 6 proposes the technique for detecting a moving velocity of a portable wireless terminal using a gyroscope installed in the portable wireless terminal.
The seventh example of the conventional techniques is disclosed in JP-A-2002-261846 identified herein as Patent Document 7 and entitled “Doppler frequency estimating apparatus, wireless device, and Doppler frequency estimating method”. The Patent Document 7 proposes the technique for calculating a Doppler frequency from a phase fluctuation and a field intensity (C/N) of a received signal with respect to a pilot symbol, and for calculating a moving velocity of a wireless device.
The eighth example of the conventional techniques is disclosed in JP-A-2004-15518 identified herein as Patent Document 8 and entitled “method of switching wireless channel connections in mobile wireless system”. The Patent Document 8 proposes the technique for constantly measuring a position of each mobile station using GPS (Global Positioning System), and for calculating a moving direction and a moving velocity of a mobile wireless system.
Patent Document 1: JP-A-7-111675 (page 18, FIG. 17).
Patent Document 2: JP-A-10-261989 (page 3, FIG. 2)
Patent Document 3: JP-A-11-98071 (page 4, FIG. 1)
Patent Document 4: JP-2669288 (pages 3-4, FIG. 2)
Patent Document 5: JP-A-2004-104223 (pages 5-6, FIG. 2)
Patent Document 6: JP-3019800 (page 3, FIG. 1)
Patent Document 7: JP-A-2002-261846 (pages 3-4, FIG. 1)
Patent Document 8: JP-A-2004-15518 (page 3, FIG. 1)